1. Field of the Invention
The invention relates to industrial shredders.
2. Description of the Prior Art
The applications of mechanical fragmentation are extremely numerous. Its purpose is to obtain a reduction in dimensions of solid bodies either to facilitate their handling or their packaging, or to enable to facilitate subsequent physical (sorting, proportioning, mixing, etc.), physico-chemical or chemical treatment.
There are also numerous types of equipment to produce fragmentation and they function by various processes such as crushing, shearing, attrition, percussion by projection or by grinding bodies, self-grinding etc. It is obvious that the choice of apparatus depends essentially on the nature of the material to be processed, on its crushing coefficients, and on its susceptibility to breakage or to agglomeration.
Even if it is relatively easy to determine the most suitable fragmentation apparatus for the treatment of a material occuring in the form of an assembly of elements having neighbouring degrees of hardness and of dimensions comprised between given limits, the fragmentation of a material formed of very dissimilar elements poses complex problems.
It is well known that fibrous, elastic or soft materials which are flexible and often tough can only be fragmented by shredding. This is the case, for example, with wood, rubber, leather, organic scraps, thermo-plastic materials, rags, old papers, stuffings, etc. Here again, when the material in bulk to be treated is in the form of an assembly of pieces of the same nature and of comparable dimensions, it is easy to define the characteristics of a blade or spike shredder enabling the desired fragmentation to be obtained. These shredders include a drum or rotor with a horizontal axis provided with shredding tools such as blades, spikes or knives which cooperate if necessary with countertools of which certain ones at least are located at the sill of the feed opening. These shredders are mostly equipped with a force-feeding device.
However, when the material is in pieces which are very different in size and in toughness, for example old papers which can include thick directories or cardboard products, it is necessary, for the purpose of obtaining homogeneous fragmentation, to provide for the possibility of effecting several cycles inside the shredder for the bulkiest and most resistant materials. A concave grate is then arranged, which surrounds the rotor towards the bottom from the sill of the feed opening thus preventing the evacuation of insufficiently fragmented elements which are then driven by the tools of the rotor to be again sheared between the latter and the countertools.
The problem and the solution are the same when there is a risk of the treated material being mixed with bodies of much greater hardness and/or toughness, such as scrap iron or various metallic materials for example. It is necessary in this case to provide a shredder having more robust tools, that is to say a shredder with knives and counter-knives acting at the same time by shearing and by percussion.
It is this same solution which must be adopted when the treated elements are very dissimilar, for example, when it is a question of processing household wastes, abatoir scraps, decanted and possibly dried sewage effluents, etc. After shredding, the fragmented material may be directed to a manual and/or mechanical sorting installation.
Thus in all cases where the material to be shredded exhibits heterogeneity of size, toughness or hardness, the shredder must include under the rotor a retaining grate, to enable recycling of oversize fragments. This is particularly important when the homogeneity of the "shredded product" is necessary for optimum subsequent utilisation, for example, for fiber separation from old papers by the wet method or again for the incineration of waste in a fluidized bed furnace.
Unfortunately, when the material to be treated contains soft and/or fibrous materials, the latter are very often wet on account of water of impregnation but also water contained in the vegetable and animal cells and cause clogging of the holes of the grate.
Experience shows that this clogging starts at the level of the downstream end of the grate, expecially if the counter-tools are arranged in proximity, to be propagated closer and closer in the direction of the upstream end. It has then appeared that to avoid clogging, it sufficed for the grate, instead of being concentric with the rotor, to approach the latter gradually from the feed sill to the opposite end of said grate. Excellent results have been obtained by causing the tools to pass about 40 mm. from the grate at the downstream end of the latter and to 100 or 120 mm at the upstream end.
There then exists a risk of blocking the rotor on the passage of a particularly strong and large mass since its "passageway" narrows as it advances. This risk is particularly important if household wastes are processed in which there are found at the same time fibrous or soft materials such as cardboard packages or organic materials which can cause clogging and very strong and sometimes bulky materials like metal scraps, domestic electrical appliances, etc.
Moreover, if the grate is arranged as has just been stated to avoid clogging, the shredder will not yield optimum results when used for non-clogging dry materials and may even be useless for materials such as scrap iron, slags, etc. due to jamming in the throttling neck formed at the downstream end of the grate.
It is an object of the present invention to provide an improved shredder which overcomes the aforementioned drawbacks.
It is another object of the invention to provide a polyvalent shredder device adaptable for all uses.
Other objects and advantages of the present invention will be apparent from the following description.